Some 15 metres below the cricket pitch they are cutting 15-ton blocks of stone out of the ground. There is the ‘lively’ rock (full of shells and voids left behind by sea creatures) and the base rock (the smooth creamy white stone that always struck me as being the precursor of reflective glass, so beloved of financial institutions in London: smooth, impervious, a architectural brush-off). Tom, who showed me around, has worked in the mines all his life, from the days when picks and shovels were still used. He showed me how they measure whether the roof of the mine is falling, and the curve on a graph that showed how it is quite normal for the rock above to drop by 3-4mm over the first few months, then to level out and stabilize at its slightly lower level. The idea that all the rock above was on the move was quite disturbing. But I guess what I came away with most is that mining is part of us, however unfamiliar it might be to you and me who spend our lives above ground; we have always gone underground, whether to paint pictures, excavate diamonds, draw out fossil fuels (such as coal), for protection (I also visited a military bunker today), or to bury our dead. It made me realise that Portland is so much about the relationships between the surface and what is underneath. Artist are meant to be skilled at thinking laterally, but here it is vertical, sedimentary, thinking that is needed.